The invention relates to an assembly for a thin-film optical device comprising a substrate and a plurality of elongated banks arranged on the substrate and spaced apart to form a plurality of channels for receiving a substance.
The invention further relates to an organic electroluminescent display device and to a method of manufacturing an electroluminescent display device.
Such an assembly, display device and method are known from, for example, EP 0 989 778 A1, which discloses a substrate for patterning thin film and surface treatment thereof. The banks partition areas on the surface of the substrate, which are to be coated with a substance comprising, for example, an electroluminescent material. To prevent overflow of the substance between adjacent areas, upper surfaces of upper portions of the banks have liquid droplet reservoir structures. The banks must therefore be wide enough to accommodate such reservoirs, which must have a large enough cross-section to absorb all of the spillover between the areas. The banks detract space from the area available for channels that could otherwise be filled with an organic electroluminescent compound to create the pixels of the display device. This is especially problematic when adjacent channels are to be filled with compounds emitting light of a different colour, and a high resolution of the image displayed is to be achieved.
It is an object of the present invention to provide an alternative assembly, display device and method of manufacturing a display device of the type mentioned above.
Accordingly, the assembly according to the invention is characterised in that at least one channel widens locally at at least one position along that channel to define a site for depositing a quantity of the substance. The method according to the invention is characterised by selecting an assembly according to any one of claims 1-5, and depositing one or more quantities of a substance comprising an organic electroluminescent material only at deposition sites along a channel.
Thus, it is possible to use closely spaced channels with a small width relative to the droplet diameter to achieve a high resolution of the image displayed. Because the quantities are deposited as droplets only at sites where the channel is wider, spillover between adjacent channels is prevented.
In a preferred embodiment of the assembly according to the invention, each channel widens locally at a plurality of positions along that channel to define a plurality of sites for depositing quantities of the substance. Thus, it is possible to deposit different optical substances in different channels to create a multi-colour display device, without any mixing occurring between the different substances.
In a preferred variant of this embodiment, parallel deposition sites of adjacent channels are staggered relative to each other. Thus, the total width of adjacent channels in a multi-colour display manufactured from the assembly can be kept small so as to achieve a high resolution.
In a preferred embodiment of the assembly according to the invention, facing sides of the banks forming a channel have a section at least partially overhanging the channel. Thus, an increased capillary effect causes fluid deposition in droplets at the depositing sites to better fill the channel sections between the deposition sites.